Electrolytic plating apparatus and process



D. E. VARNER 2,895,888

ELECTROLYTIC PLATING APPARATUS AND PROCESS 4 Sheets-Sheet 1 July 21,1959 Filed 001:. 7. 1957 HSNOdSI-IU 801331.30

INVENTOR DONALD E. VARNER July 21, 1959 D. E. VARNER ELECTROLYTICPLATING APPARATUS AND PROCESS Filed Oct. .7, 1957 4 Sheets-Sheet 2 M m xT No N9 in m M N9 0 w M m2 a I 8. k E & mi D w W g D g 02 m o o: u E flwwfl I Tom mmE 2.0mm Mm: moo Em July 21, 1959 D. E. VARNER 2,395,888

' ELECTROLYTIC PLATING APPARATUS AND PROCESS Filed 001:. 7, 1957 Q 4Sheets-Sheet 3 INVENTOR mm P DONALD E. VARNER 11, v, kiiiiii'iiiiiii L B122/ July 21, 1959 Y D. E. VARNER 2,895,888 ELECTROLYTIC PLATINGAPPARATUS AND PROCESS Filed Oct. 7, 1957 4 Sheets-Sheet 4 INVENTCRDONALD E. VARNER "jig-5 United States Patent ELECTROLYTIC PLATINGAPPARATUS AND PROCESS Donald E. Varner, Columbus, Ohio, assignor toIndustrial Nucleonics Corporation, a corporation of Ohio ApplicationOctober 7, 1957, Serial No. 688,720

14 Claims. (Cl. 20428) This invention relates to control apparatus forcontinuous electrolytic plating lines such as electrolytic tinning orzinc plating lines, and more specifically it relates to an automaticregulating system for maintaining constant a predetermined thickness ofplating electrodeposited on a base material; in accordance with directmeasurements of the plating thickness per se.

Present techniques for achieving automatic regulation of platingthickness are in general based upon the fact that the quantity of metalelectrodeposited on a base material is a function of the plating timeand the density of the plating current. Accordingly automatic platingthickness controls now applied to continuous electroplating lines aredesigned to maintain a constant ratio of the current density to thespeed of the workpiece through the plating tanks. of such control ispredicated on the existence of certain constant factors directlyaffecting these tWo basic variables which cannot in fact be maintainedconstant under practical conditions.

To illustrate the practical difiiculty of achieving precise line speedregulation, consider a high-speed tinning line where strip steel iscoated at speeds approaching 2,000 feet per minute through the platingbaths. The processing unit comprises not just one machine, but anintegrated plurality of different types of machines requiring elegantlycomplex automatic controls for speed synchronization between mainsections and portions thereof. The various sections simultaneously workon a continuous strip of steel on the order of a thousand feet inlength. There is an ever-present necessity throughout the line forcareful control of strip tension within the narrow limits required forsuccessful strip tracking, guiding and coil centering, as Well as toprevent looping, stretching or tearing of the strip. Control of loopstorage between sections lends further However, the accuracy intricacyto the problem of speed synchronization, as

does the requirement for coordinated acceleration and deceleration amongthe various units of the process line. Although every attempt is made tohold line speeds to predetermined values and to synchronize all drivensections as well as plating current regulation devices to the speed ofthe strip through the plating baths per se, it is apparent that theaccuracy of the speed control in fact suffers an appreciable degree ofdependence on the conditions necessary to the maintenance of these otherlimiting factors.

Similarly, problems are attendant on the precise control of platingcurrent density, which must be correlated not only with line speed butwith changing strip widths and plating efficiencies. In addition,leakage currents of substantial intensity tend to by-pa-ss the flow ofworking plating current; these leakage currents being characterized bychangeable magnitude depending on the amount of moisture and/orspattered electrolyte solution distributed around and about the vicinityof 2,895,888 Patented July 21, 1959 .responsive to the potential dropsacross shunts which are apt to change resistivity with temperature,while .the heavy currents combined with a corrosive atmos phere resultin changing contact potentials contributing to errors in current densitymeasurements.

In addition to the difficulties attendant on these vari able factorswhich adversely affect the accurate determination and maintenance ofspeed and current density, other problems arise in securing the properbasic combinations thereof. At present, plating currents in relation tovarious factors such as line speed, plating thickness specification,material, sheet Width and the like are arrived at by calculation,modified by statistical analyses of past production, and often summarilyaltered at the discretion of an experienced plater. The correctness of agiven combination of settings can only be proven by a directdeterminating of the actual plating thickness obtained thereby.Generally, plating thickness is measured by laboratory tests on samplesof the product taken at infrequent intervals. Those tests which canpresently be relied on for accuracy are usually variations of either anelectronic electrostripping method or a chemical dissolution of theplating and subsequent titration of the dissolved metal salt. Thesemethods are rather slow and laborious, so that after a sample is takenon the line considerable time elapses before the test results are known,and during this long delay capable of providing accurate andsubstantially instantaneous direct readings of the thickness of aplating on a base material; such a measuring device which is capable ofrendering its readings in a continuous manner on the actual productionline and under production conditions, and an automatic regulating systemutilizing such an instrument as a sensing element for maintaining aproperly balanced condition among the several variables above describedso as to assure the application of a uniformly correct thickness ofplating under all conditions of line operation.

In accordance with a first preferred embodiment of this invention, theaccuracy with which existing controls are able to maintain a constantpredetermined plating thickness is monitored by a master regulatingfeedback loop governed by direct plating thickness measurements on thetraveling strip; said measurements being provided by a nuclear betaradiation reflection gauging device. On the basis of such measurementcontinuously provided by the gauging instrument, the set point of theconventional plating current regulating apparatus is automaticallyreadjusted as required, to the end that the plating thickness ismaintained substantially constant at any desired absolute value,regardless of changes in any or all of a plurality of error-producingvariables of the type described hereinabove. By this means it has beenfound possible to achieve a degree of control accuracy quiteunattainable with prior control methods, resulting in appreciable rawmaterial savings and a substantially better quality plate.

In another form of the invention which comprises an extension of thefirst embodiment, a pair of gauging devices are used to measurerespectively the plating thicknesses on opposite sides of a platedstrip. The indicated thicknesses are then added by means of a summationcomputer to provide a reading of total plating thickness, and a commonregulator controlling bottom and top plating currents is automaticallyadjusted in accordance with any error observed in said total platingthickness.

In still another preferred embodiment, independent current regulatorsare provided for respectively controlling the plating on the top andbottom sides of a plated strip. These regulators are automaticallycontrolled independently in accordance with respective measurements oftop and bottom plating thicknesses. This system is particularlyapplicable to differential plating processes.

In special cases, the requirements of a particular process are such thatit is desirable to maintain the plating current substantially constant,and to vary the line speed through the plating baths in order to therebyregulate the amount of plating applied. Hence in another embodiment ofthe present invention, automatic control of line speed regulation iseflected in accordance with measured values of the plating thickness,thereby to maintain said thickness relatively constant at a desiredvalue.

It is an object of this invention to provide an improved method formaintaining constant a desired thickness of plating electrodeposited onan elongated workpiece passed in continuous fashion through a platingbath.

It is also an object to provide a system for controlling a continuousplating operation in accordance with direct measurements of platingthickness. It is another object to provide a control system inaccordance with the above objects incorporating a measuring means ofgreatly increased accuracy and reliability.

It is still another object to provide means for continuouslyre-evaluating the ratio of plating current to the speed of a workpiecethrough a continuous plating bath, and for automatically correcting saidratio incident to an error therein.

It is a further object to provide an automatic control system for acontinuous electrolytic strip plating process whereby the sum of theplating thicknesses on opposite sides of the strip can be maintainedsubstantially constant at a desired value.

It is a still further object to provide a control system for adifferential plating process line whereby plating thicknesses applied toopposite sides of a plated strip are regulated independently inaccordance with direct measurement of the respective thickness values.

.It is an additional object to provide a control system in accordancewith the above objects which is easily adapted forconvenientinstallation on a variety of existing electroplating lines with littleor no modification thereof, andfurther, to provide such a system whichis relatively economical to build and to install; requiring a minimum ofadjustment and maintenance.

Other objects and advantages of the invention will become apparent inthe following detailed description given with reference to theaccompanying drawings, in which: Figure 1 is a schematic showing of anillustrative continuous plating line; specifically a high speed tinplate line controlled by direct feedback of plating thicknessmeasurements in accordance with this invention.

Figure 2 is a simplified schematic diagram illustrating operationaldetails of an apparatus designed to meet the requirements of a preferredsystem of control in accord-.

ance with the invention.

Figure 3 is a modification of the apparatus of Fig. 1, showing anotherpreferred embodiment of the invention wherein plating current isautomatically regulated in accordance with variations in the speed ofthe line; the action of the speed responsive current regulating meansbeing governed in turn by master control means respon 'sive to platingthickness measurement.

Figure 4 shows a system for controlling a sheet metal plating line inaccordance with the sum of the plating 5 thicknesses on opposite sidesof the sheet.

Figure 5 illustrates the control of differential plating apparatus inaccordance with the invention.

Figure 6 is a showing of a plating line in accordance with a furtherembodiment of the invention wherein plating thickness is controlled byvarying the speed at which the workpiece travels through the platingtanks. Figure 7 is a sketch illustrating the measurement of platingthickness by the beta radiation reflection method in accordance with theinvention.

Figure 8 is a graph relating detector response to beta radiationreflected from plated and unplated surfaces.

Referring to Figure 1, there is shown a typical continuous platingapparatus incorporating a basic preferred form of the present invention.For purposes of illustration, ahorizontal halogen type of tin plate lineis here 'idepicted, although it will be understood that any one ofseveral. different types of continuous electrolytic plating "processesmay be served as well by the incorporation therewith of the system ofthe invention. The numeral 10 here indicates a workpiece to be plated,consistingin this example of a steel strip supplied from a coil 12. Whenthe coil 12 is depleted, its trailing end and the leading end of anothercoil 14 are joined in the 'splicer 16 whichcomprises a double-cut shearand welder.

301Thus successive coils are fed to the machine in the form ofacontinuously advancing strip. While the splicing operation is inprogress, the machine is supplied with strip from one or more storageloops as at 18, which H are refilled when the splice is completed byaccelerating the entry section to speeds greater. than that of theplating section.

The numeral 20 generally indicates processes which prepare the strip forplating, such as cleaning, scrubbing and pickling. From here the stripenters the bottom plating tank, shown at 22, thence passing to the topplating tank 24. To electrodes (not shown) disposed in these platingtanks, plating current is supplied through bus leads 26 and 28respectively from a plurality of generators 3040. In a post-platingsection 42, electrolyte solution adhering to the strip 10 is recoveredand the plated strip is cleaned and dried. The strip thence passesthrough a reflow tower 44 comprising a furnace or resistive heatingapparatus wherein applied heat causes the plating to flow or melt on thesurface of the strip, producing a bright finish and nonporous coating.At 46 is an after-treatment section of some type wherein the surfaces ofthe flow-brightened sheet are given further cleaning, chemical treatmentand/or oiling as required to prevent later formation of oxides or stainsthereon. The 'loop storage unit 48, together with the shear 50 and reels52 and 54 comprise the delivery section of the plating line. Referringto the center section in which the plating operation isv accomplished,the plating generators 30-40 supply plating current to the tanks 22. and24 in accordance with the setting of a current regulator which in turncontrols the output of an exciter generator 62 supplying voltage to thefield circuits of generators 3040. It will be understood that thisparticular set-up is' merelyexemplary, and that any one of severalpossi- 5 ble arrangements may be employed using either a single platinggenerator or multiple units of conventional design controlled by any oneof several known types of current regulating apparatus. The drive,system for the strip transport machinery and the control devicestherefor are not shown in view of their complexity and known character.Rather, it is sufiicient to assume in this instance that the speed ofthe strip 10 through the plating tanks 22 and 24 can be maintainedrelatively constant, and

' that theregulator 60 is able to maintain the plating current at aconstant value determined initially by the 3 setting of the manualcontrol 64. The control 64 is set by the operator or plater according toavailable figures relating a desired plating thickness, sheet width andstrip speed to current density required.

In accordance with this invention, the coarse current regulator control64 is supplemented by a relatively fine" control which may take the formof a taper rheostat 66 adapted for motorized adjustment by automaticelectromechanical means responsive to any deviation in the measuredplating thickness from a predetermined value.

The direot measurement of plating thickness necessary to this system ofcontrol is provided by a nuclear radiation reflection gauging instrumentcomprising an inspection head 70 and a console unit 72 connected by amulticonductor cable 74. This instrument is preferably of the type whichis fully described in a co-pending application, Serial No. 662,672,filed May 31, 1957, by George B. Foster and William R. Clore, andaccordingly the full details thereof are omitted from thisspecification. The console 72 of the instrument contains a strip chartrecorder 76 having an indicating pen and pointer mechanism 78 whichregisters the actual plating thickness with reference to an associatedscale 80.

The recorder .also includes a target indicator assembly comprising atarget pointer 82 which may be positioned relative to the scale 80 bymeans of a mechanically coupled target setting knob 84. The targetadjustment is used by the operator to set a desired value of platingthickness to be maintained constant by the automatic controller 90.Whenever the indicating pointer is not in alignment with the targetpointer, an error signal is transmitted to the controller. In accordancewith an error signal received, the controller 90 will energize anactuator motor 92, which drives the rheostat 66 through the agency of aspeed reduction gear box 94, thereby resetting the plating currentregulator 60 to increase or decrease the current output of generators30-40 as required to restore the plating thickness to the target value.

The controller fit) may be designed in accordance with well-knownprinciples, and may be embodied in any one of a great variety of formsknown to persons skilled in the art. Controllers found by applicant tohave suitable characteristics for elfectively carrying out theoperational details incidental to the practice of the invention may beclassified into two general types. One type is referred to as acontinuous or integrating controller such as is described in aco-pending application Serial No. 657,434, filed May 6, 1957, by RichardF. Warren. The other is a reset type controller, incorporating means forproportioning each corrective adjustment to the magnitude of the errorsignal and providing means for suspending control action after eachadjustment until material plated in accordance with the adjustedsettings has reached the measuring station. A simplified form of thelatter preferred type of controller is shown in the schematic diagram ofFigure 2.

Referring to Figure 2, the underscored numerals 1tltl- 103 locatedmarginally of the drawing designate sections thereof picturing relatedelements grouped insofar as possible according to function. At 100 is acomparator bridge circuit; at 102 is an error sensing circuit; at 104 isan actuator motor control circuit; section 196 is designated an on timecircuit and section 1% is designated an off time mechanism.

The comparator bridge 1% comprises a pair of potentiometers 110 and 112connected across a DC. power source represented by the battery 114. Thevariable taps of these potentiometers are mechanically coupledrespectively to the measuring pointer 78 and the target pointer 82 ofthe recorder 76 in a manner such that there is no potential differencebetween the taps when the pointers are in mutual alignment. However,when the measuring pointer 78 deviates from the target thicknessindication represented by theposition of the target pointer 82, avoltage appears on line 116, connected to the tap of potentiometer 110,which voltage has a polarity in accordance with the direction of thedeviation and an amplitude proportional to the magnitude thereof; Thisvoltage is taken with reference to line 118, which is connected to thetap of potentiometer 112, and pro vides the error signal input to theerror sensing 102 and on time 106 circuits.

In the error sensing section 102 the error signal ap pears across asensitivity setting potentiometer 120. portion of the signal appearingon the variable tap of potentiometer is fed into an integrating circuitcomprising a capacitor 122 and a rheostat 123 which provides anadjustable time constant. The integrated signal on capacitor 122 is thenamplified by an inverse feedback stabilized amplifier 124 having aninput resistor 126 and feedback resistor 128. The function of relaycontacts 2112b and resistor 204 will be described hereinafter.

Referring now to the motor control section 104, it is seen that theoutput of amplifier 124 is connected across the coil 130 of a sensitiveelectromechanical switching device such as a contact meter or polarizedrelay so as to drive a dynamic contact member 136a, which has a range ofmovement between limits established by the stationary contacts 1311b and1300. Contacts 13811-1300 are in circuit between voltage supply lines132 and 134 which may be connected across the conventional 115 V. AC.power source 136. These contacts function to selectively operate a pairof output relays 138 and 140 which control the operation of the actuatormotor 92.

The motor 92 is a two-phase motor with a pair of windings 92a and 92bboth connected directly at one end to the common line 134 and coupled atthe opposite ends through the phase shifting network combination ofresistor 142 and capacitor 144. These windings may receive power fromline 132 either through contacts 138a or contacts 140a of the respectiveoutput relays 138 or 140. When contacts 138a close, this power isapplied directly to winding 92a, whereas winding 92b is energizedthrough the phase shift network 142 and 144, causing the motor 92 to runin one direction. When contacts 140 a close instead, line voltage isapplied directly to winding 92b and to winding 92a shifted in phase sothat the motor runs in the opposite direction. As hereinabove describedin connection with Figure l, the motor 92 actuates the taper rheostat 66through gear box 94.

The contacts 13tPa-13tlc of the switching device 131), the output relays138 and 149, as well as contacts 138b, 138a, 1411b and 1400 may receivepower from lines 132 and 134 only by way of line 146, which is connectedto line 132 through normally closed contacts 1511a of relay and normallyopen contacts 148a of a time delay relay 148. Relay 148 receives powerfrom lines 132 and 134 through normally closed contacts 202a of relay2112. The functioning of relays 150 and 2112 will be more fullydescribed hereinafter.

Assuming that the time delay relay 148 is energized through contacts202d, and that contacts 148a are therefore closed, as are contacts 150a,line 146 is connected to line 132. Hence the dynamic contact 1313a ofthe switching device 130 may receive power through contacts 138a and1400. Therefore when the output of the error sensing device 1112 exceedsa predetermined value in one direction, switch contact 130a willenergize relay 138 through contact 1301). Similarly, if the error is inthe other direction relay 141 will be energized t trough contact 1300.

Once an output relay is energized, it will remain so independently offurther action by switch 130. This is, if relay 138 is energized, itscontacts 13812 will close, establishing a holding circuit for the coil138 through contacts 140a. instantaneously thereafter contacts 1380remove power from switch arm 130a, preventing relay 140 from becomingenergized in the event that a chance reversal of the error signalpolarity should cause the arm 130a to make contact with 1300. Similarlyif relay 140 is energized, its contacts 1401; will provide a holdingcircuit for its coil and contacts 140s will prevent operation of relay138. Accordingly, through the agency of relay contacts 138a or 140a,when the actuator motor 92 is placed in operation it will continue torun in the same direction until the controlling output relay isde-energized by removal of power from line 146, which is efiected byopening relay contacts 150a.

The length of time the motor 92 is permitted to operate, and hence themagnitude of the corrective adjustment applied to the taper rheostat 66,is regulated by the on time proportioning device 106. Basically thissection comprises an electronic timer which is automatically set to timeout at the end of an interval of time determined by the magnitude of theerror signal on line 116. At the end of this interval power to theactuator motor 92 is switched off by operation of the on time relay 150whose contacts 150a mentioned above remove power from line 146 whichsupplied the voltage for operating the output relays 138 and 140.

Relay 150 is connected in the plate circuit of a thyratron tube 152which is supplied with power from lines 132 and 134; the cathode 154 ofthe thyratron being normally disconnected, however, from line 134 bynormally open contacts 138d and 140d of the output relays 138 and 140.The control grid 156 is connected by way of a grid stopper resistor 158to a timing circuit comprising a capacitor 160 and a rheostat 162. Thetiming circuit is energized by the error signal on line 116, which isconnected through resistor 164 to the input of a rectifier bridge 166.The rectifier bridge has an output in accordance with the magnitude ofthe error signal, but due to the depolarizer action of the rectifierthis output always has the same polarity as indicated, whether the errorsignal on line 116 is positive or negative. The positive output terminalof the rectifier bridge is shown connected through a battery 168 to thecathode 154 of thyratron 152 and to one side of capacitor 160 andrheostat 162. The negative output terminal of the rectifier bridge isconnected to the other side of capacitor 160 and to the grid circuit ofthyratron 152 through normally closed contacts 138e and 140s of theoutput relays 138 and 140. Alternatively capacitor 160 may be shunted byrheostat 162 through normally open output relay contacts 138 or 140]. Inthe absence of an error signal on line 116, a negative potential justsufiicient to keep the grid 156 of the thyratron 152 at the out-oilpoint is provided by a voltage source represented by the battery 168 incircuit with the output of the rectifier bridge 166.

Normally, through resistor 164, the rectifier bridge 166, and relaycontacts 138a and 140e, the error signal voltage charges capacitor 160,so that the grid 156 of the thyratron 152 is at a negative potentialgreater than the cutofi value for the thyratron 152. The amount by whichthis bias exceeds the cut-off value is in proportion to the magnitude ofthe error signal, which has been integrated to the degree permitted bythe time constant of resistor 164 and capacitor 160.

When a corrective adjustment to the taper rheostat is initiated ashereinabove described, one of the output relays, 138 or 140 as the casemay be, locks in and holds. In the on time circuit 106 the cathode-platecircuit of thyratron 152 is then completed when contacts 138d or 140dconnect the cathode 154 to line 134. Simultaneously contacts 138a or140:: disconnect capacitor 160 and the interconnected grid circuit ofthe thyratron from the rectifier bridge output. At the same time,contacts 138 or 140] will connect rheostat 162 across capacitor 160 tostart a timing cycle wherein capacitor 160 discharges through theresistance of rheostat 162. The duration of this timing cycle depends onthe predetermined setting of rheostat 162 and the potential acrosscapacitor 160 which is in proportion to the error existing in the meas-8 ured plating thickness at the instant the corrective adjustment to thetaper rheostat 66 was initiated.

The timing cycle ends when the voltage across capacitor 160 decays tothe firing potential on the grid 156, whereupon the thyratron 152conducts current; energizing the on time relay 150 in the plate circuit.In section 104, contacts 150a of this relay open, removing power fromline 146 and de-energizing the output relay 138 or 140 which caused theactuator motor 92 to operate.

It is apparent that relay will remain energized only for a very shortinterval of time, since the contacts 138d or 140d of the output relaywhich completed the cathode plate-relay coil circuit will now reopen.

At the end of a corrective adjustment effected in the manner described,a further correction is not permitted to occur until material plated inaccordance with the new taper rheostat setting has traveled from thetank to the location of the gauging head. The travel time involved issometimes referred to as transportation lag; the duration thereofdepending on the line speed. This lag is conveniently determined bymeans of an automatically resetting odometer type device adapted toprovide a signal indicating the passage of a predetermined length of thetraveling material.

The illustrative device depicted in section 108 of Figure 2 comprises anelectromagnetic counter which opens an electrical circuit uponaccumulating a predetermined member of electrical pulses provided by aninterrupter switch the interrupter being operated by a cam 172 which isdriven in suitable speed relation to the linear velocity of thetraveling workpiece 10, as through a coupling 173 to a roll 174 intractive engagement with the workpiece. The counter per se may include asolenoid having an armature 176 which is magnetically withdrawn'into acore 178 against the tension of a spring (not shown) upon application ofa suitable voltage to the solenoid coil 180. A continual opening andclosing of the coil circuit therefore results in a series ofreciprocatory oscillations of the armature 176, which are converted bythe ratchet mechanism 182 to a stepwise and clockwise unidirectionalrotation of the shaft 184. Shaft 184 is arranged to drive a furthercoaxially extending shaft 186 through an electrically actuated clutch188. The clutch 188 rigidly couples shafts 184 and 186 when a suitablevoltage is applied to line 190, which line comprises one lead of theclutch coil (not shown); the other lead thereof being connected to line134. Accordingly, when the clutch is electrically energized, the ratchet182 may drive the shaft 186 clockwise against the counter-torque of aspring 192 which circumvents the shaft 186 in a flat spiral and isadapted to rotate the shaft in a counterclockwise direction when theclutch 188 is disengaged by disconnecting the source of electric powertherefrom. A portion of the shaft 186 is threaded to accommodate atraveling nut 194 which is also carried on a smooth, stationary guiderod 196. The nut 194 bears a switch actuator lug 198 adapted to trip anormally closed electrical switch 200 when the nut 194 has advanced asufiicient distance in the direction indicated by the arrow. The switch200 is in circuit with the coil 202 of a relay adapted to be energizedfrom lines 132 and 134.

The 011 time, or transportation delay system 108 is placed in operationat the instant the on time relay 150 is energized to terminate anadjustment to the taper rheostat 66. Contacts 150b of this relay thenconnect the coil of relay 202 to line 132 through contacts of the switch200. When relay 202 is energized, its contacts 202a close, providing aholding circuit for the coil 202 when contacts 150]; of the on timerelay subsequently reopen. Other contacts of relay 202 disable thecontroller circuits as follows:

In section 102, contacts 202b short-circuit the input to the errorsensing amplifier 124 through shunt resistor 204. In section 106,contacts 202c short-circuit the error signal into the rectifier bridge166 through shunt resistor 206.

In section 104, contacts 202d remove power from the time delay relay148, whose contacts 148a in turn disconnect relay contacts 150a and line146 from line 132, thus preventing operation of output relays 138 and140 even though contacts 150a re-close. These disabling conditions aremaintained for the duration of the transportation delay, which isdetermined as follows:

When contacts 202e of relay 202 close, the clutch 188 is energized,coupling shaft 184 to shaft 186. Contacts 202@ also energize theinterrupter switch 170, whose contacts close and reopen once each time apredetermined length of material 10 passes over roll 174. Each contactclosure energizes the solenoid coil 180 and each reopening de-energizesit, so that the resulting oscillation of the spring-loaded armature 176produces an incremental clockwise rotation of shaft 186 and a slightmovement of the traveling nut 194 in the direction of the limit switch200. As these operations are repeated, the total movement of the nut 194comprises a tally of the number of unit lengths of material 10 whichhave passed the roll 174. When this tally represents a predeterminednumber of such lengths, the switch 200 is operated, de-ener gizing theoff time relay 202. As contacts 202a now open, power is removed from theclutch 188, allowing the spring 192 to unwind, rotating shaft 186counterclockwise and driving the traveling nut 194 to the rear until thestrike pin 210 carried thereby engages the radially projecting arm 212which is secured to the shaft 186 to limit the extent of thecounterclockwise movement thereof.

When relay 202 is de-energized, all circuits of the controller arerestored to the original condition, except for the contacts 148a of thetime delay relay 148, which contacts do not close immediately uponapplication of power to the relay through contacts 202d. It is thepurpose of the time delay relay to permit the counter mechanism insection 10 8 to reset itself fully before a subsequent correction to thetaper rheostat setting can be allowed to begin. When contacts 148a closeafter a short delay to permit spring 192 to fully unwind, anothercorrection to the plating current regulator may occur if an error in theplating thickness is still present.

The counter dial mechanism 214 is provided to permit adjustment of thecounter in accordance with the linear distance traveled by the workpiece10 between the tank 22 and the gauging head 70. See Figure 1. The dialsetting determines the distance the nut 194 must travel from itsstarting position until the lug 198 opens switch 200. The switch 200 iscarried by a further traveling nut 216 on the threaded shaft 218, whoseangular setting may be changed by rotating the dial, through settinggears 220 and 222.

While the control system of Figure l is very effective on a processwherein the line speed can be maintained relatively constant, noprovision is made for effecting the immediate changes in the platingcurrent density which must occur concommitantly with changes in the linespeed. Such provision is featured in the system of Figure 3, which showsthe center section of the electroplating line of Figure 1 incorporatinga control system which is outwardly almost identical with the controlsystem of Figure 1. In this case, however, the system is modified by thesubstitution of current regulator 300 for the regulator of Figure 1, andby the addition of a tachometer 302 which is driven at a rateproportional to the linear speed of the workpiece 10 through the agencyof a roll 304 in tractive engagement with the workpiece. The regulator300 may be any one of several types presently employed in theelectroplating industry; for example, a regulator system such as isdescribed in US. Patent No. 2,325,401, issued July 27, 1943, to GeorgeJ. Hurlston. Accordingly a detailed description herein of the regulatorper se is deemed unnecessary.

It is the purpose of the regulator 300 to maintain a constant ratio ofplating current to line speed. Such a ratio is initially determined byone or more manual adjustments of the current controller. Thereafter, inthe operation of the system, if the line speed is increased, the currentdensity is increased proportionally. If the line speed decreases, theregulator responds by immediately and proportionally decreasing thecurrent density. This system has the advantage of being able tocompensate immediately for an undesirablechange in the plating thicknesswhich would otherwise accompany a change in the line speed, whereas inthe system of Figure 1 there would be a considerable delay(transportation lag) before the gauging head 70 observed an error in theplating thickness as the basis for corrective action.

In Figure 3 the taper rheostat 66 comprises a fine adjustment of the setratio relating line speed to current density. The controller 90,responsive to an error in the actual plating thickness, may thereforemodify the predetermined ratio of line speed to current density, therebyautomatically compensating for calculation errors, erroneous readings ofthe speed or current measuring devices, drifts in the regulator 300, ora variety of other error producing variables such as are describedhereinabove.

Figure 4 illustrates a further embodiment of the invention wherein theoutput of the plating generators is controlled in accordance with thesum of the plating thicknesses on opposite sides of a sheet or strip ofbase material. Herein a further gauging head 350 and interconnectedrecording unit 352 are employed to provide a measurement of the platingthickness on the top side of the strip. This measurement appearsdirectly on the scale of the recording unit 352, and may readily becompared with the measurement of the bottom plating thickness presentedon recording unit 72. Although separate recording units are shown forsimplicity, it may be advantageous to employ a dual recording instrumentwhereby both measurements are inscribed in contrasting colored inks on acommon strip chart.

In addition to recording the respective bottom and top platingthicknesses, the instruments 72 and 352 are adapted to provideelectrical voltage analogs thereof on lines 354 and 356. These analogsare electrically added by a summation computer 358, which preferablycomprises a conventional servomotor rebalancing potentiometer networkequipped with a recording mechanism which provides a visual indicationand strip chart record of the sum of the readings on instruments 72 and352.

In the event that the gauging heads 70 and 350 may be necessarilylocated some distance apart, a delay device is preferably incorporatedin the circuit whereby the signal on line 354 is delivered to thecomputer 358. The delay unit preferably comprises a memory track 360passing under a recording head 362 energized by the signal on line 354.The memory track is driven in suitable speed relation to the movement ofthe workpiece 10 by means of a mechanical coupling or synchro tierepresented by the dotted line 364 which is connected to a roll 366 intractive engagement with the workpiece. The recorded thicknessindicating signal is thus carried on the memory track 360 at a rate suchthat the signal arrives at a pickup head 368 at the same instant that asignal representing the plating thickness on the opposite side of anidentical part of the workpiece 10 is present on line 356. Thus the twothickness measurements added by the computer 358 at any given instantare taken at substantially the same spot along the length of theworkpiece 10. The signal transmitted to the pickup head 368 issubsequently erased from the memory track at the point where said trackpasses under an erasing head 370.

The error signal input to the controller in this case is derived fromthe recording computer 358 in the same fashion as hereinabove describedin connection with Figure 1 and Figure 2.

In Figure 5, there is depicted an electroplating line f the type shownin Figures 1, 3 and 4 which is adapted which is justified, for example,in the production of tin plate to be used in the manufacture of tincans, which require a heavy coat of tin on the inside thereof to resistfood acids, etc., whereas only a sufficient thickness of tin to preventrusting for a reasonable length of time is necessary on the outside.

In the horizontal tinning line whose center section is shown in Figure5, the bulk of plating applied to the strip in tank 22 is deposited onthe bottom side of the strip, whereas in tank 24 the bulk of the platingis deposited on the top side. The respective thicknesses are detectedindependently by the gauging heads 70 and 350, the measurements beingpresented on recording instruments 72 and 352.

Generators 30-34 are operated independently to supply current to thebottom plating tank 22, whereas generators 36-40 supply only the topplating tank 24. In this case, the outputs of the two groups ofgenerators are independently controlled, generators 30-34 being providedwith a separate exciter 62a and regulator system 300a, whereasgenerators 36-40 are provided with exciter 62b and regulator system 30%.

Regulator 300a is in turn controlled by the system of this invention,utilizing gauging head 70, instrument 72, controller 90a, motor 92a,gear box 94a and taper rheostat 66a associated with regulator 300a.Similarly another master regulating feedback loop controls regulator300b, utilizing gauging head 350, instrument 352, controller 90b, motor92b, gear box 94b and taper rheostat 66b.

In some instances, it is more practical to maintain a constant platingcurrent, while controlling the plating thickness by varying the linespeed. Such is the case, for example, in certain alkali plating lineswhere current densities are limited to a very narrow range ofpermissible values. Accordingly, Figure 6 depicts the center section ofa representative alkali plating line controlled by the system of thepresent invention. Herein a strip 400 or other workpiece to be plated ispicked up from a storage loop 402 by traction means comprising a drivebridle 404, and passed successively through a pickling tank 406, aplating tank 408, an electrolyte recovery tank 410, a rinse tank 412, adryer 414 and thence under a guide roll 416 and through a further drivebridle 418. Through the tanks 406-412, the strip is carried onfestooning rollers as at 420 distributed within and outside the tanks.To the electrodes (not shown) disposed in plating tank 408, current issupplied from a conventional plating generator 422 controlled by aconstant current regulator 424 through the agency of the excitergenerator 426. The principal driving means for transporting the strip isprovided by the bridles 404 and 418, powered by drive motors 430 and432. The interaction of these dynamic elements also provides theprincipal means for maintaining proper tension on the strip. Motors 430and 432 are energized by a generator 434, and are under control of amore or less complex line speed and tension regulating apparatus 436. Inview of the conventional nature and complexity of device 436, thedetails thereof are appropriately omitted from this specification,although reference can be made to one form of such apparatus which isdescribed in US. Patent No. 2,264,277, issued December 2, 1941, toWillard G. Cook. This apparatus includes a speed control rheostat 438whereby the line speed setting may be adjusted.

In order to apply the control system of this invention to the process,the rheostat 438 is modified to permit driving the same byelectromechanical means. The master speed regulating control isessentially the system depicted in Figure 1, and comprises theinspection head 7 0,

CAD

recording instrument 72, controller 90, actuator motor 92 and gear box94, which function as described in connection with Figure 1. Thus if theplating thickness on the strip 400 passing under roll 416 past thegauging head 70 is excessive, rheostat 438 is automatically reset toincrease the line speed in proportion to the extent of the platingthickness deviation. Conversely, if the measured thickness of theplating is inadequate, the line speed is decreased.

Although the control system of this invention is illustrated herein asemploying a nuclear radiation reflection gauge, it is apparent thatother types of gauging instruments may be employed. Methods known toapplicant which have been heretofore proposed for continuously gaugingthe thickness of plating are of two types; namely, an electromagneticmethod and an X-ray fluorescence method. As a practical matter, however,both these methods appear to suffer from inherent difficulties whichhave not as yet been resolved to the point where a production typeinstrument can be designed to meet the standards of accuracy andstability prerequisite to the acceptance thereof as a sensing element ina self-regulating industrial process.

The difliculties of electromagnetic methods are apparent in that theydepend on amplitude or phase angle measurements involving magneticreluctance paths which are subject to change due to temperature, wear ofmechanical parts contacting the strip, and variable electromagneticproperties of the strip itself as a result of variations in materials,work hardening, or magnetic or thermal treatment thereof.

There are several variations of the X-ray fluorescence method. One ofthese variations depends for its results on precise angularrelationships which are very difficult to maintain in an instrumentadapted for use on a production line. Another requires a ratherimpractical procedure of selective detection of the pertinentfluorescence Wave lengths in the presence of a continuous spectrumand/or a variety of other monochromatic components. The third requiresthat photon energies of the primary radiation beam should be sufiicientto produce resonance absorption in the base material but not high enoughto excite resonance in the plating; a condition possible of achievementin the case of tin plating on steel but rather impractical in a casesuch as that of zinc plating on steel. In any case, the primaryradiation required is in the low kilovolt range, and unfortunatelysuitable radioactive isotopes for providing photon radiations in thisenergy range are not available. Accordingly, the fluorescence methodsrequire the use of X-ray tubes, whose ray outputs are notoriously sosubject to instabilities and dependence on external variables as topreclude absolute calibration or precise reproducibility of instrumentreadings; at least for purposes of continuous measurement underindustrial conditions. It is therefore necessary to effect some kind ofcomparison between the indication produced by the measured material andthe indication produced by some kind of plated material sample. By sucha comparison, an accurate reading can admittedly be obtained when thetwo indications are identical. The difficulty arises when the twoindications differ from one another, because it cannot be determinedwith certainty just how much the measured thickness deviates from thestandard thickness. It is readily apparent that the how much" is reallythe all-important quantity in the self-regulation of the process,because this quantity determines the extent of the correctiveadjustments which must be effected by the automatic controller.

In the beta radiation reflection method, no critical angles areinvolved, so that the detector is permitted a wide acceptance angle forhigh efliciency. The detection and measurement may be completelynon-selective. The radiationsource may consist of a beta emittingradioisotope whose ray output is supremely steady and constant; beingsubject only to a very slow, gradual decline in intensity as essence theradioisotope decays according to its half-life scheme. This gradualdecline may easily be compensated for by periodic standardization,wliich may be readily carried out by fully automatic means. Thus theinstrument can maintain an absolute calibration, requiring no comparisonstandard or involved set up procedure in order to effect a measurement.

A basic apparatus for beta reflection measurement of plating thicknessis shown in Figure 7. Herein a detector 500 comprises an ionizationchamber having a conducting outer wall 502 forming an anode and aninsulated metallic probe 504 forming a cathode. In circuit with thedetector 500 are a voltage source 506, measuring circuitry indicatedgenerally at 508 and an indicator 510. The chamber encloses a radiationsource 512 comprising a small quantity of a beta emitting radioisotopewhich is contained in a source holder 514 having thick shielding wallsfor preventing direct radiation from the source from entering thechamber. An opening in the bottom side of the holder 514 directs a beamof beta radiation outwardy from the source/detector assembly. A thinwindow 516 allows beta radiation reflected from an object placed in thepath of said beam to return to the interior, active detecting portion ofthe chamber. There is also shown a material strip 518 comprising a thinlayer of plating metal P deposited on a base metal B.

Figure 8 shows a group of curves relating the response of detector tovarious material samples placed in front of the source/ detector unit.It will be noted that when there is no material in front of the source/detector, the detector response is not zero, but shows some value 1,, asa result of various factors such as scattered radiation or radiationreflected from air in front of the detector. Curves M and M respectivelydepict the effects of placing increasing thicknesses of pure basematerial and pure plating material in front of the source/detector. Inboth instances, at some generally indeterminate thickness T.,, referredto as in infinite thickness, the detector responses attain maximumvalues 1;; and I respectively. Beyond Tm a further increase in thicknessproduces no change in response. The values of I and 1; are eachempirically proportional to the ratio 2 A where Z is the atomic numberof a material and A is the atomic weight thereof. Where there is asignificant difference between the value of this ratio for the basematerial and its value for the plating material, very accuratemeasurements of plating thickness can be made where the base material isheavier than an infinite thickness and the plating is lighter than aninfinite thickness. Fortunately, these conditions obtain in mostcontinuous plating processes, provided that the proper choice of theradioactive source is made. Examples of preferred isotopes for thispurpose are strontium-90, krypton-85 and thallium-204.

The small graph superimposed on the large graph of Figure 8 shows thedetector response curve I as a function of an increasing thickness ofplating such as zinc or tin applied to a greater-than-infinite thicknessof base material such as steel strip.

While the invention is herein shown and described as embodied inspecific systems and particular apparatus, it will be understood thatsuch showing and description is given by way of example only, and thatmany other different system combinations and rearrangements as well asapparatus modifications can be made without departing from the spiritand scope of the invention as is set forth in the appended claims.

What is claimed is:

1. The method of electrodepositing a controlled thickness of plating ona continuous length of base material, which comprises conveying saidbase material lengthwise at a controllable rate through a plating bath,supplying said bath with a plating current of controllable magnitude fordepositing a thickness of said plating material on said base material toform a plated material, initially maintaining a predetermined ratio ofsaid current magnitude to said conveyor rate, removing electrolytewetting a surface of said plated material traveling away from said bath,directing a beam of beta radiation into said traveling surface,quantitatively detecting reflected beta radiation returned backwardlyfrom said surface to provide an indication of the thickness of platingon said surface, and correctively altering said ratio whenever saidthickness indication deviates from a desired value.

2. The method of electrodepositing a controlled thick ness of plating ona continuous length of base material, which comprises conveying saidmaterial lengthwise through a plating bath, supplying said bathinitially with a plating current of predetermined magnitude fordepositing a thickness of plating material on said base material to forma plated material, removing electrolyte adhering to a surface of saidplated material traveling away from said bath, directing a beam of betaradiation into said traveling surface, quantatively detecting reflectedbeta radiation returned backwardly from said surface to provide anindication of the thickness of plating on said surface, and readjustingthe magnitude of said plating current whenever said thickness indicationdeviates from a desired value.

3. The method of electrodepositing a predetermined thickness of platingon a continuous length of base material, which comprises conveying saidmaterial lengthwise through a plating bath, supplying said bathinitially with a plating current of predetermined magnitude fordepositing a thickness of plating material on said base material to forma plated material, removing electrolyte adhering to a surface of saidplated material traveling away from said bath, directing a beam of betaradiation .into said traveling surface, quantitatively detectingreflected beta radiation returned backwardly from said surface to renderan indication of the thickness of plating on said surface, comparingsaid rendered thickness indication with said predetermined thickness toprovide a difference indication, and correctively readjusting themagnitude of said plating current by an amount proportional to saiddifference indication.

4. Electrolytic apparatus for depositing a controlled thickness ofplating on a continuous length of base material, comprising means forconveying said base material lengthwise through a plating bath, drivemeans for said conveyor means, a current source supplying platingcurrent to said bath for depositing a thickness of plating material onsaid base material to form a plated material, means for removingelectrolyte adhering to a surface of said material traveling away fromsaid bath, means for directing a beam of beta radiation into saidtraveling surface, means for quantitatively detecting reflected betaradiation returned backwardly from said surface to render an indicationof the thickness of plating on said surface, means for comparing saidrendered indication with a predetermined thickness indication to providea difference indication, means for adjusting the speed of said drivemeans, and means responsive to said difference indication for actuatingsaid speed adjusting means.

5. Electrolytic apparatus for depositing a predetermined thickness ofplating on a continuous length of base material, comprising means forconveying said base material lengthwise through a plating bath, acurrent source supplying plating current to said bath for depositing athickness of plating material on said base material to form a platedmaterial, current regulator means responsive to the speed of saidconveyor means for controlling the output of said current source so asto maintain said output proportional to said conveyor speed, means forremoving electrolyte adhering to a surface of said plated materialtraveling away from said bath, means for directing a beam of betaradiation into said traveling surface, means for quantitativelydetecting reflected beta radiation returned backwardly from said surfaceto render an indication of the thickness of plating on said surface,means for comparing said rendered indication with said predeterminedthickness to provide a difference indication, means for adjusting saidcurrent regulator means, and control means responsive to said differenceindication for actuating said adjusting means.

6. Electrolytic apparatus for depositing a controlled amount of platingon a continuous length of base sheet material, comprising means forconveying said base material lengthwise through a plating bath, acurrent source supplying plating current to said bath for depositing athickness of plating material on opposed first and second surfaces ofsaid base material to form first and second plated surfaces, means foradjusting the ratio of the speed of said conveyor to the magnitude ofsaid plating current,

means for removing electrolyte adhering to said first and second platedsurfaces traveling away from said bath, first and second meansrespectively for directing a beam of beta radiation into each of saidtraveling surfaces, first and second means respectively forquantitatively detecting reflected beta radiation returned backwardlyfrom each of said surfaces to provide first and second indicationsrespectively of the thickness of plating on said first and second platedsurfaces, means for adding said first and second indications to render atotal indication, means for comparing said total indication with apredetermined indication to provide a difference indication, and controlmeans responsive to said difference indication for correctively alteringthe setting of said ratio adjusting means.

7. Electrolytic apparatus as in claim 12 wherein said second detectingmeans is spaced from said first detecting means in the direction ofmovement of said plated material, and wherein said adding means includesmeans for recording said first indication and means for reproducing thesame for addition to said second indication after a delay equal to thetime required for a discrete portion of said plated material to travelfrom said first detecting means to said second detecting means.

8. Differential plating apparatus for electrolytically depositing acontrolled thickness of plating material on each of the two opposedsides of a continuous length of base sheet material, comprising meansfor conveying said base material lengthwise through a plating bath, afirst current source supplying plating current to said bath fordepositing a first thickness of plating material on a first surface ofsaid base material to form a first plated surface, means for adjustingthe current output of said first current source, means for registering afirst predetermined value for said first thickness; means responsive tosaid first thickness of plating on said first plated surface of saidmaterial issuing from said bath for rendering an indication of saidfirst thickness, said first thickness responsive means including meansfor directing a beam of beta radiation into said first plated surfaceand means for quantitatively detecting refiected beta radiation returnedbackwardly therefrom; means for comparing said rendered indication withsaid registered indication to provide a first difference indication,means responsive to said first difference indication for actuating saidoutput adjusting means for said first current source, a second currentsource supplying plating current to said bath for depositing a secondthickness of plating material on a second surface of said base materialopposed to said first surface to form a second plated surface, means foradjusting the current output of said second current source, means forregistering a second predetermined value for said second thickness,means responsive to said second thickness of plating on said secondplated surface of said material issuing from said bath for rendering anindication of said second thickness; said second thickness responsivemeans including means for directing a beam of beta radiation into saidsecond plated surface and means for quantitatively detecting reflectedbeta radiation returned backwardly therefrom; means for comparing saidlast-mentioned rendered indication with said last-mentioned registeredindication to provide a. second difference indication, and meansresponsive to said second difference indication-for actuating saidoutput adjusting means for said second current source.

9. The method of electrodepositing a controlled thickness of platingmaterial on a continuous length of base material, which comprisesconveying said base material lengthwise at a controllable rate through aplating bath, supplying said bath with a plating current of controllablemagnitude for depositing a thickness of said plating material on saidbase material to form a plated material, obtaining a measurement of saidthickness by directing a beam of beta radiation into the surface of saidplated material during the passage thereof away from said bath andquantitatively detecting reflected beta radiation returned backwardlyfrom said surface, and readjusting the ratio of said current magnitudeto said conveyor rate whenever said thickness measurement deviates froma predetermined value.

10. The method of electrodepositing a controlled thickness of platingmaterial on a continuous length of base material, which comprisesconveying said base material lengthwise through a plating bath,supplying said bath initially with a predetermined plating current fordepositing a thickness of plating material on said base material to forma plated material, obtaining a measurement of said thickness bydirecting a beam of beta radiation into the surface of said platedmaterial during the passage thereof away from said bath andquantitatively detecting reflected beta radiation returned backwardlyfrom said surface, and readjusting said plating current whenever saidthickness measurement deviates from a predetermined value.

11. Electrolytic apparatus for depositing a predetermined thickness ofplating on a continuous length of material, comprising means forconveying said material lengthwise through a plating bath, a currentsource supplying plating current to said bath, means for adjusting thecurrent output of said source, means for directing a beam of betaradiation into a surface of said material issuing from said bath, meansfor quantitatively detecting reflected beta radiation returnedbackwardly from said surface to render an indication of the thickness ofplating on said surface, means for comparing said rendered indicationwith said predetermined thickness to provide a difference indication,means for generating an electrical signal proportional to saiddifference indication, and control means responsive to said signal foractuating said current output adjusting means.

12. Electrolytic apparatus for depositing a controlled thickness ofplating material'on a continuous length of base material, comprisingmeans for conveying said base material lengthwise at a controllable ratethrough a plating bath, a current source for supplying a plating currentof controllable magnitude to said bath for depositing a thickness ofsaid plating material on said base material to form a plated material;means responsive to the thickness of plating on said plated materialissuing from said bath for rendering a plating thickness indication,said thickness responsive means including means for directing a beam ofbeta radiation into a surface of said plated material and means forquantitatively detecting reflected beta radiation returned backwardlyfrom said surface; means for registering a predetermined thicknessindication, means for comparing said rendered indication with saidregistered indication to provide an electrical signal having acharacteristic proportional to the difference therebetween, means foradjusting the ratio of said current magnitude to said conveyor rate,motor means for actuating said adjusting means, means responsive to apredetermined value of said signal characteristic for initiatingoperation of said motor means, means for terminating said motoroperation when the movement of said adjusting means produced by saidmotor means is proportional to said signal characteristic, and meansenergized upon termination of said motor operation for disabling saidmotor operation initiating means for the time required for a discretepor- 17 tion of said plated material to travel from said bath to saidthickness responsive means.

13. Electrolytic apparatus as in claim 11 wherein said motor operationterminating means comprises a timer operative for an interval functionalof said signal characteristic, and switch means actuated by said timerat the end of said interval for removing power from said motor.

14. Apparatus as in claim 13 wherein said disabling means comprisesmeans for accumulating a count of unit lengths of said plated materialpassing a reference point, switch means for disabling said motoroperation initiating means during the accumulation of said count, andmeans for actuating said switch means when said count exceeds apredetermined number.

References Cited in the file of this patent UNITED STATES PATENTSHurlston July 27, 1943 Rendel July 15, 1952 Rendel Apr. 20, 1954 Bachmanet a1 Feb. 14, 1956 Korbelak et al Mar. 5, 1957 Rendel Jan. 14, 1958FOREIGN PATENTS Canada. Sept. 21, 1954 UNITED STATES PATENT OFFICECERTIFICATE OF CORRECTION Patent No, 2,895,888 July 21, 1959 Donald E,Varner It is hereb$ certified that error appears in the -printedspecification of the above numbered patent requiring correction and thatthe said Letters Patent should read as corrected below.

Column 14, line 18, for "qualitatively" read quantitatively column 15,line 28, for the claim reference nwneral "12" read 6 column 17, line 3,for the claim reference numeral "ll" read u l" Signed and sealed this9th day of February 1960.,

Attest:

.AXLINE ROBERT C. WATSON Commissioner of Patents Attesting Officer

1. THE METHOD OF ELECTRODEPOSITING A CONTROLLED THICKNESS OF PLATING ONA CONTINUOUS LENGTH OF BASE MATERIAL, WHICH COMPRISES CONVEYING SAIDBASE MATERIAL LENGTHWISE AT A CONTROLLABLE RATE THROUGH A PLATING BATH,SUPPLYING SAID BATH WITH A PLATING CURRENT OF CONTROLLABLE MAGNISTUDEFOR DEPOSITING A THICKNESS OF SAID PLATING MATERIAL ON SAID BASEMATERIAL TO FORM A PLATED MATERIAL, INITIALLY MAINTAINING APREDETERMINED RATIO OF SAID CURRENT MAGNITUDE TO SAID CONVEYOR RATE,REMOVING ELECTROLYTE WETTING A SURFACE OF SAID PLATED MATERIAL TRAVELINGAWAY FROM SAID BATH, DIRECTING A BEAM OF BETA RADIATION INTO SAIDTRAVELING SURFACE, QUANTITATIVELY DETECTING REFLECTED BETA RADIATIONRETURNED BACKWARDLY FROM SAID SURFACE TO PROVIDE AN INDICATION OF THETHICKNESS OF PLATING ON SAIOD SURFACE AND CORRECTIVELY ALTERING SAIDDRATIO WHENEVER SAID THICKNESS INDICATION DEVIATES FROM A DESIRED VALUE